Attorney General Eric Holder announced this week that both the crime rate and the prison population have dropped over the last year, indicating that "longer-than-necessary" sentences don't improve public safety.

In a speech Tuesday in New York City, Holder said the Justice Department expects to end the current budget year next week with a prison population of roughly 215,000 inmates, a figure that's down roughly 4,800, according to The Associated Press. It would be the first time since 1980 that the federal prison population has declined during the course of a fiscal year.

In addition, internal figures from the Bureau of Prisons show a projected drop of more than 2,000 inmates in the next year, and nearly 10,000 in the year after.

"This is nothing less than historic," Holder said, addressing a conference at the New York University School of Law that was hosted by the Brennan Center for Justice. "To put these numbers in perspective, 10,000 inmates is the rough equivalent of the combined populations of six federal prisons, each filled to capacity."

The crime rate has dropped along with the prison population, Holder said, proving that "longer-than-necessary prison terms" aren't always effective.

"In fact, the opposite is often true," he said.

With policies that have at times unsettled prosecutors and others in law enforcement, Holder has worked in the last year to reduce a prison population he says is costly and bloated. The Bureau of Prisons accounts for roughly one-third of the Justice Department budget, and the number of inmates has exploded in the last three decades as a result of "well-intentioned policies designed to be 'tough' on criminals," Holder said.

In August 2013, for instance, he announced a major shift in sentencing policy, instructing federal prosecutors to stop charging many nonviolent drug defendants with offenses that carry mandatory minimum sentences. More recently, the Justice Department has encouraged a broader swath of the prison population to apply for clemency, and has supported reductions in sentencing guideline ranges for drug criminals that could apply to tens of thousands of inmates.

"We know that over-incarceration crushes opportunity. We know it prevents people, and entire communities, from getting on the right track," Holder said.

Holder also said that there should be new ways for the government to measure success of its criminal justice policies beyond how many people are prosecuted and sent to prison.

In this era, he said, "It's no longer adequate — or appropriate — to rely on outdated models that prize only enforcement, as quantified by numbers of prosecutions, convictions, and lengthy sentences, rather than taking a holistic view."

The Brennan Center, a public policy and law institute, issued a report Tuesday urging new success measures for U.S. attorney offices, including examining changes in the local violent crime rate, changes in the recidivism rate, and the percentage of violent crime cases on the docket compared with the previous year.

Attorney General Eric Holder announced this week that both the crime rate and the prison population have dropped over the last year, indicating that "longer-than-necessary" sentences don't improve public safety.